Coating method of fertilizer

ABSTRACT

A COATED GRANULAR FERTILIZER IS MANUFACTURED BY COATING A SOLID FERTILIZER WITH A COATING PREPARATION WHICH COMPRISES A WATER-SOLUBLE RESOL TYPE PHENOL RESIN HAVING WATER TOLERANCE OF ONE OR GREATER, AN ORGANIC ACID HAVING A DISSOCIATION CONSTANT NOT EXCEEDING 2X10**-4 AND A FILLER SUCH AS TALC AND THEN HARDEN THE COATING COMPOSITION BY HEATING AT 100-130*C.

United States Patent US. CI. 71-64 F 7 Claims ABSTRACT OF THE DISCLOSURE A coated granular fertilizer is manufactured by coating a solid fertilizer with a coating preparation which comprises a water-soluble resol type phenol resin having water tolerance of one or greater, an organic acid having a dissociation constant not exceeding 2X and a filler such as talc and then harden the coating composition by heating at 100-130 C.

REFERENCE TO RELATED APPLICATION This is a continuation-in-part of our copending application Ser. No. 705,272, filed Feb. 14, 1968, and now abandoned.

BACKGROUND OF THE INVENTION This invention relates to a coated granular fertilizer and a manufacturing method therefor.

Recently, increasing attention is being given to coated fertilizers prepared by coating the surface of fertilizer grains with, for example, synthetic resin so as to restrict the dissolution of the fertilizer and ensure controlled release of its fertilizing components.

However, the resins heretfore known as usuable for the coating of fertilizer have many drawbacks. For example, they require the use of expensive solvents and, therefore, tend to increase the production cost; they involve a highly complicated coatitng procedure; and the surface of fertilizer particles to be coated therewith is vulnerable to cracking.

A main object of the present invention is to provide a fertilizer coating method which makes it possible to easily control the release of the fertilizing components.

Another object of this invention is to provide an inexpensive, uniformly coated fertilizer.

Still another object of this invention is to provide a coated fertilizer which has superior Water resistance and which is not vulnerable to cracking even after being in the soil for along time.

SUMMARY OF THE INVENTION In the coating preparation of the present invention the viscosity of a water-soluble resol type phenol resin is raised and the formation in the product of fine pores of appropriate size is ensured by the addition of a filler such as talc, silica powder, white carbon or wheat flour which does not react with said resin. To hasten the harding of the resin there is further added as a catalyst an organic acid such as acetic acid or oxalic acid whose dissociation constant does not exceed 2 x 10- Phenol resins can be roughly classified into the resol type and the novolak type in accordance with the ratio of formalin to phenol, kinds of catalyst, etc. used.

Phenol resin used in the present invention is condensed water-soluble resol type phenol resin having a water tolerance of one or greater which is produced by reacting 100 parts of phenol and 130-300 parts of formalin in the presence of caustic soda as a catalyst. Not only can this resin be used, as it is without being dissolved in an organic solvent but it is also low in cost and very safe from fire and explosion. Where instead of the aforementioned phenol resin, vinyl acetate resin or urea resin is used, there are likely to occur cracks which allow the fertilizer to dissolve quickly thus making controlled release impossible.

However the phenol resin used in the present invention lacks viscosity and when it is used alone for coating the fertilizer, the greater part thereof seeps into the fertilizer. Therefore, a sufficient coating is not formed. So as to increase the viscosity of the resin and thereby ensure the formation of fine pores of appropriate size in the coating of the product, there is added to the resin a filler such as talc, wheat flour, silica powder or White carbon which does not react with the resin. When the fertilizer thus coated is put in the soil, Water contained in the soil gradually enters the fertilizer from the innumerable pores formed in the coating thereby dissolving the fertilizing components which gradually pass into the soil.

With a view to determining how the ratio of tiller to resin affects the rate at which the fertilizing components dissolve and flow out of the fertilizer, talc was added at different ratios between 0.5 and 30 parts to 10 parts of water-soluble phenol to produce five coating preparations. Each of the said preparations was used to twice coat the surface of a solid fertilizer (egg-shaped, 40 g. each) by the brush coating method, and the solid fertilizer was heated at C. for 60 minutes to allow the coating to harden. Each sampling thus obtained was wrapped in cotton gauze, placed on a metal support, submerged in a beaker filled with 1 l. of distilled water and allowed to stand. A S-ml. sampling was taken every other day over one week from the liquid held in each beaker and the rate of release was calculated on the basis of the weight of the dried fertilizing components contained therein.

The results of this experiment are shown in Table 1.

TABLE 1 Release rate (percent) after- Parts of tale to 10 parts phenol resin 1 day 3 days 5 days 7 days 19. 9 40. 5 60. 5 64. 7 19. 5 43. 62.6 68. 6 19. 4 39. 0 56. 6 62. 0 19. 3 43. 6 61.0 68. 0 19. 3 46. 6 70. 0 74. 7 19. 4 46. 8 52. 7 65. 3 18. 6 39. 2 58. 2 62. 5 18. 7 45. 2 60. 5 71. 2 19. 2 42. 3 63. 8 68. 6 As the coating preparation becomes a paste, coating cannot be efiected From the preceding table, it is evident that even if the filler is added at a high ratio, there is seen almost no change in percentage released and the coating preparation is therefore effective. However, if 30 parts filler are added, the coating preparation fails to form a coating on the fertilizer and is therefore unusable.

Although water-soluble phenol resin will harden in a shorter time if heated under pressure, the application of pressure is undesirable in the case of fertilizer coating. As, however, it is important from an industrial point of view to shorten the hardening time, the present inventors conducted experiments to find a catalyst appropriate for speeding up the hardening process. Experiments were conducted using, as catalysts, such inorganic acids as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid and such organic acids as formic acid, acetic acid, butyric acid and oxalic acid. All acids except formic acid, acetic acid and butyric acid were found to have the following drawback: They showed such strong catalytic action that the resin was hardened in a matter of a few seconds at room temperature, making the coating operation extremely ditficult. Moreover, the coating formed consequently repelled water, underwent shrinkage and lacked water-resistance.

By contrast, when formic acid, acetic acid or butyric acid was used as a catalyst, the hardening reaction proceeded only very slightly at normal room temperature and The coating preparation made of 10 parts of watersoluble phenol resin, 2 parts of talc and 0.2 part of acetic acid was spread twice with a writing brush on egg-shaped solid fertilizer samples (each weighting 40 g.), which were thereafter heated at the different temperatures of 100 the resin did not separate from water. Perfect hardening 5 C., 110 C., 120 C. and 130 C. for 60 minutes. By folof the coating was achieved by heating. lowing the procedure of the experiment of Table 1, the The coating formed on the surface of fertilizer in the release rate for fertilizing component was determined of presence of such catalyst enjoys a fair degree of flexibility each coated fertilizer sample. The thickness of the coatand abounds in water-resistance. ing formed was 200,12.

Of the various organic acids, oxalic acid exhibits dif- TABLE 3 ferent properties from those of formic acid, acetic acid and butyric acid as mentioned above. After conducting a Release rate (Percent) after study, it was clear that the difference is related to 2 7 16 26 30 the dissociation constant of such acids. That is to 5 Temperature'oc' days days days days days say, formic acid (HCOOH) has a dissociation co1i 100 1.2 5.2 20.5 43.3 50.1 stant of 2 10 acetic acid (CH COOH) i9 1o g-g 3-3 f3 g-g g-Z butyric acid (CH (CH COOH) l.5 l0- and oxalic 0:3 0:8 1:9 2:9 4:3 acid ((COO'H) 4 10 When representative acids having a dissociation constant below 4x10 such as acrylic 2 The preceding table shows that, in the range of hardenacid, crotonic acid, iso-crotonic acid, succinic acid, glyg temperatures of to the coating colic acid, lactic acid and so forth were subjected to the quired an increased degree of hardening and g nsame test as performed on acetic acid, they showed a hanced restriction of release in proportion to the rise of similar trend. In consideration of the ready availability temperature. Although the highest temperature used in this and inexpensiveness, however, acetic acid is preferable 2 experiment was 130 C., the degree of hardening may be industrially. heightened further at higher temperatures such as more Now, an explanation is made of the quantity of such than in View Of the boiling Point of the OPgaflie organic acid to be added, as a catalyst, to the wateracid to be usedsoliible phenol resin. As mentioned hitherto, the coating of the fertilizer is To the mixture having 2 parts of talc incorporated into 30 Carried Out by a dipping method, a brush coating method, 10 parts of water-soluble phenol resin, acetic acid was etc., but it may be eifected by the following method. At added at the different ratios of from 0% to 6% of the the first step, the fertilizer is put in a rotating drum. phenol resin to produce three coating preparations. Then, a proper amount of the coating preparation is These preparations were deposited in three different a ed drop by drop to the d um as it rotates. When the ways: (a) one coating by dipping method, (b) two coatpreparation has stuck to the whole surface of the fertilings by dipping method and (0) one coating by the brush heat is pp ther e130- method. The hardening was carried out by heating at DESCRIPTION OF PREFERRED 130 C. for minutes. The rate of release was determined by the same method as d fo h experiment f Table 1. 40 The following examples are further illustrative of this The rates of release determined for the coated fertilizer invention, and it Will be understood that the invention is samples after being left to stand for one week are shown not limited theretoin Table 2. Example 1 TABLE 2 A mixture consisting of 10 parts water soluble phenol Tm kn Rat o of added acetic acid o Phenol resin resin, 2 parts talc and 0.2 part acetic acid was spread of c atiii percent) evenly over the surface of solid fertilizer (egg-shaped: 40 Sample (I5 0 0- 0-5 2 4 6 g. each) by the brush coat method. This coating was 1 0 100 7 825 7 7 81.1 SOlldlfiEd at 120 C. 01 60 minutes to fOIlIl a TWO (10) 1 100 7 5 50 samples, (A) and (B), were selected and their rates of 100 100 100 2 8&9 release were measured. The results are given below:

TABLE 4 Days 134578111418242731 Sample:

(A),percent 1.1 14.7 19.8 27.9 37.3 42.5 52.1 57.7 65.1 70.2 74.6 80.9 (B),percent 0.8 16.8 18.9 23.6 31.2 35.9 45.6 52.7 57.9 64.3 68.4 74.5

Table 2 indicates that the rate of release of the fertilizer varies with the percentage of acetic acid added. In the sample wherein no acetic acid was used, the hardening was insufiicient and all fertilizer dissolved. In case of 0.2% acetic acid, almost no hardening was effected.

As can be seen from the above table, the best controlled release characteristics are obtained with percentages of acetic acid ranging from 0.5 to 6 wt. percent.

As explained above, there is a relationship between the amount of catalyst added and the hardening time. It is natural that the higher the amount of the added catalyst, the shorter the hardening time. The amount of the added catalyst, therefore, may be selected in accordance with the purpose of use.

A description is given hereinafter of the relationship between the hardening temperature of coating preparation and the release rate for fertilizer.

Example 2 Test material (A) Non-coated solid fertilizer.

(B) Solid fertilizer coated by the method of this example.

(C) Solid fertilizer coated with the same mixture as used in this example but with the talc replaced by the same volume of wheat flour.

TABLE 5 Days 1 2 7 17 21 28 Sample:

(A), percent 58. 6 73. 2 97. 2 100 (B), percent 1.1 1. 9 2. 4 3. 3 3. 5 10. 2 percent 1. 9 2.1 s. 4 11. e 20. 0 24.4

Example 3 Three coating prepartions were obtained by respectively adding 0.2 part formic acid, 0.2 part butyric acid and 0.2 part lactic acid to a mixture of 10 parts watersoluble phenol resin and 2 parts talc. Each coating preparation thus prepared was used to twice coat the surface of solid egg-shaped fertilizer and then hardened by heating at 120 C. for 60 minutes. The results are shown in Table 6.

Test materialkg. of a high analysis compound fertilizer (N: 12.4%, P 0 12.3%, K 0: 12.5%, diameter of particle: 4-6 mm.) was put in a coating drum of the inclination type. Then, 200 g., 400 g. and 600 g. of coating preparation comprising parts water-soluble resol type phenol resin, 0.2 part acetic acid and parts talc were respectively sprayed onto the fertilizer while rotating the coating drum at 30 rpm. After coating, the coating, prepartion was hardened at 120 C. for 60 minutes. A release test was conducted as to the products obtained according to this example. The results was shown in the following table.

TABLE 7 Release rate (percent) after- 1 14 21 24 Amount of coating (percent) day days days days days Analysis method: 15 g. of the sample were put into a 500 ml. Erlenmeyer flask. 300 ml. of water having a temperature of 30 C. was added to the sample and the sample was then left in a constant temperature bath at a temperature of 30 C. Ammonium nitrate was analyzed and the release rate was obtained in accordance with the following equation.

Rate of release What is claimed is:

1. A coated granular fertilizer comprising a granular fertilizer,

a hardened coating on the surface of said granular fertilizer and having a plurality of fine pores in the coat- 111g,

said coating comprising a hardened mixture of:

10 parts water-soluble phenol resin having a water tolerance of one or greater, 0.05 to .6 part of at least one organic acid having a dissociation constant not exceeding 2 10 and 0.5 to 25 parts of filler.

2. The coated granular fertilizer, as set forth in claim 1 wherein the organic acid is one selected from the group of formic acid, acetic acid and butyric acid.

3. A method for coating fertilizer comprising the steps of applying to solid fertilizer particles a coating preparation comprising a water-soluble phenol resin having a water tolerance of one or greater, an organic acid having a dissociation constant not exceeding 2 l0- and a filler and then solidifying said coating preparation by heating it to a temperature betwen 100 C. and C.

4. The method, as set forth in claim 3, wherein the organic acid is one selected from the group of formic acid, acetic acid and butyric acid.

5. The method, as set forth in claim 4, wherein about 0.050.6 part organic acid is added to 10 parts resin.

6. The method, as set forth in claim 3, wherein 0.5-25 parts filler is added to 10 parts resin.

7. The coated fertilizer, as set forth in claim 1, wherein said resin is a resol type pheno-formaldehyde resin.

References Cited UNITED STATES PATENTS 3,223,518 12/1965 Hansen 71-64 2,411,557 11/1946 Schuh 260-59 2,665,221 1/ 1954 Grandgaard 11716l X 2,734,002 2/1956 Schoeld et al. 117-100 2,870,039 l/1959 McReynolds 117100 X 2,967,789 1/1961 Hoyt 1l7-l00 2,992,124 7/1961 Campbell 117-161 3,083,118 3/1963 Bridgeford 117-100 X 3,325,276 6/1967 Feller 71--64 3,369,884 2/1968 Barton 71-64 X FOREIGN PATENTS 1,087,009 10/ 1967 Great Britain 11716l WILLIAM D. MARTIN Primary Examiner D. C. KONOPACKI, Assistant Examiner US. Cl. X.R.

117100 A, B, 161 L 

